It didn't happen on chrome so I checked on Safari.
Safari has issues with sub pixel rendering and anti aliasing. That's what's happening here.
When an element is in motuon, it can't be antialiased at the same time, and the sub pixel rendering is also turned off. On some browser and certain conditions, especially when the moving element is lower in z than the rest of the page, the antialiasing and/or sub pixel rendering of the other elements is also turned off.
Solution one doesn't work on everything but must be tested first): give a higher z-index to the element in question
Solution 2: add this custom code to force antialias and/or sub pixel rendering
/* webkit css animation flickering fix*/
-webkit-font-smoothing: antialiased !important;
font-smoothing: antialiased !important;
.class-of-the-elementby the class of your element.